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Why is My 12 Volt Battery Reading as 13 Volts?

Inside diagram of Lead acid battery

All Lead acid batteries (Gel, AGM, Flooded, Drycell, etc) are made up of a series of 2.2 volt cells that are bridged together in series to reach their final desired voltage. For instance, a 6 volt battery will have 3 cells (3 x2.2= 6.6 volts), a 12 volt battery will have 6 cells (6 x2.2=13.2 volts) and so on.That 2.2 volts is the fully charged, straight off the charger number. The actual resting voltage, or the voltage a battery will settle at 12-24 hours after being removed from the charger, is closer to 2.1 volts per cell, or about 6.4 volts for a 6v battery, and 12.7 volts for a 12v battery. These numbers assume 100% healthy cells, and may vary a bit lower for older batteries.

3 Responses,   5.0 Rating

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  • Very helpful information and well-written for a non-technical college grad. Thank you

    April 23, 2012 a 9:02 am
    • I have 6 8volt batteries that are dead. My charger won‘t charge them because they are below 20 %. and they are 5 years old. Can they be saved?

      January 21, 2013 a 11:22 am
      • If the 8 volt charger won‘t do it, try using a 6 volt charger to bring them up to the point where the 8 volt charger can ‘read them’ and turn on.

        January 21, 2013 a 12:20 pm
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